1. Field of the Invention
This invention relates to lasers which produce a high average power. Such structures of this type, generally, produce the high average power intensity having a high peak intensity at a wavelength near 530 nm.
2. Description of the Related Art
Several schemes are in use for frequency doubling a solid-state laser specifically a Nd:YAG laser. A pulse-pumped, Q-switched oscillator, optionally followed by a similarly pumped single pass amplifier and an external SHG (second harmonic generation) crystal is the most commonly used scheme. While high peak powers can be generated with this approach, the repetition rate, and hence also the average power, are severely limited.
Significantly higher repetition rates are achievable if intracavity SHG is used. This technique provides a high conversion efficiency, but since it excludes the addition of optical amplifiers, the extractable output power is restricted to the power available from the oscillator, and the chance for a further scale-up is forfeited.
The third possibility is "external resonant doubling" and is used mainly for CW lasers. This approach is technically more demanding than the others because it requires a single-axial-mode oscillator and the frequency-locking of a "slave" resonator to a "master" resonator. Since resonant doubling is, strictly speaking, a method to enhance the SHG efficiency it does not specify how the fundamental beam is produced (except that it has to be single-mode). These cases are the modi operandi that produce extremely long pulses, either because of a very high Q-switch repetition rate, or because the laser is not Q-switched, which includes true CW operation as the limiting case. Therefore, a more advantageous laser system, then, would be presented if the average power could be increased while maintaining a high peak power.
It is apparent from the above that there exists a need in the art for a laser system which produces a high average power and a high peak power, and which at least equals the average and peak power characteristics of known lasers but which at the same time is applicable to practically all known operating modes of lasers, ranging from true CW, CW-pumped modelocked or Q-switched, to pulse-pumped free-running or Q-switched, with the modulated-output-power modes spanning a range of repetition rates from single shot to 100 MHz. It is a purpose of this invention to fulfill this and other needs in the art in a manner more apparent to the skilled artisan once given the following disclosure.